1. Field
The disclosed embodiments relate to the field of communications, and more particularly, to communications using quadrature amplitude modulation.
2. Background
Multilevel modulation may be used in communications of digital signals. In a multilevel modulation technique, the modulation level of each point in a constellation representing the modulation is fixed during the modulation process. One of the multilevel modulation techniques is commonly known as quadrature amplitude modulation (QAM). In QAM, the constellation may be represented by an equidistant constellation. The points in an equidistant constellation are arranged in a way in the constellation such that the distance between two adjacent points for all the points in the constellation is equal. The distance between the points represents an amplitude difference in the multilevel modulation process.
A receiver receiving a signal modulated in accordance with a QAM technique relies on information relating to the amplitude difference or the distance between each point in the constellation to demodulate the received signal. Often times, the amplitude difference or the distance between each point is communicated to the receiver via a digital word with a finite number of digits. In a system, where the distance between each point in the constellation may be changing from one transmission to another, the receiver communicates the updated value periodically. The value of the amplitude difference or the distance between each point in the constellation may fall between the values that the digital word can represent due to a finite quantization. Therefore, the transmitter may not be able to communicate an exact value of the amplitude difference or the distance between each point in the constellation. Such a quantization error may lead to inaccuracy in the demodulation process, and resulting in poor performance.
To this end as well as others, there is a need for an improved communication system.
In a communication system, a method and an accompanying apparatus provide for efficient modulation and demodulation processes. In a transmitter, a ratio of power level of a communication channel over power level of a pilot channel is determined to produce a power level ratio. The power level ratio is quantized within a finite digital word. A quantized quadrature amplitude modulation distance, in a quadrature amplitude modulation constellation, is determined from the quantized power level ratio, and the quantized ratio is communicated to a receiver. A signal, in accordance with a quadrature amplitude modulation technique, is modulated using the quantized distance.